/*
 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk/module-main/src/main/java/org/apache/http/message/LineFormatter.java $
 * $Revision: 573864 $
 * $Date: 2007-09-08 08:53:25 -0700 (Sat, 08 Sep 2007) $
 *
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.message;

import org.apache.http.Header;
import org.apache.http.ProtocolVersion;
import org.apache.http.RequestLine;
import org.apache.http.StatusLine;
import org.apache.http.util.CharArrayBuffer;

/**
 * Interface for formatting elements of the HEAD section of an HTTP message.
 * This is the complement to {@link LineParser}. There are individual methods
 * for formatting a request line, a status line, or a header line. The
 * formatting does <i>not</i> include the trailing line break sequence CR-LF.
 * Instances of this interface are expected to be stateless and thread-safe.
 * 
 * <p>
 * The formatted lines are returned in memory, the formatter does not depend on
 * any specific IO mechanism. In order to avoid unnecessary creation of
 * temporary objects, a buffer can be passed as argument to all formatting
 * methods. The implementation may or may not actually use that buffer for
 * formatting. If it is used, the buffer will first be cleared by the
 * <code>formatXXX</code> methods. The argument buffer can always be re-used
 * after the call. The buffer returned as the result, if it is different from
 * the argument buffer, MUST NOT be modified.
 * </p>
 * 
 * 
 * @author <a href="mailto:rolandw AT apache.org">Roland Weber</a>
 * 
 * 
 *         <!-- empty lines above to avoid 'svn diff' context problems -->
 * @version $Revision: 573864 $ $Date: 2007-09-08 08:53:25 -0700 (Sat, 08 Sep
 *          2007) $
 * 
 * @since 4.0
 */
public interface LineFormatter {

    /**
     * Formats a protocol version. This method does <i>not</i> follow the
     * general contract for <code>buffer</code> arguments. It does <i>not</i>
     * clear the argument buffer, but appends instead. The returned buffer can
     * always be modified by the caller. Because of these differing conventions,
     * it is not named <code>formatProtocolVersion</code>.
     * 
     * @param buffer
     *            a buffer to which to append, or <code>null</code>
     * @param version
     *            the protocol version to format
     * 
     * @return a buffer with the formatted protocol version appended. The caller
     *         is allowed to modify the result buffer. If the
     *         <code>buffer</code> argument is not <code>null</code>, the
     *         returned buffer is the argument buffer.
     */
    CharArrayBuffer appendProtocolVersion(CharArrayBuffer buffer,
            ProtocolVersion version);

    /**
     * Formats a request line.
     * 
     * @param buffer
     *            a buffer available for formatting, or <code>null</code>. The
     *            buffer will be cleared before use.
     * @param reqline
     *            the request line to format
     * 
     * @return the formatted request line
     */
    CharArrayBuffer formatRequestLine(CharArrayBuffer buffer,
            RequestLine reqline);

    /**
     * Formats a status line.
     * 
     * @param buffer
     *            a buffer available for formatting, or <code>null</code>. The
     *            buffer will be cleared before use.
     * @param statline
     *            the status line to format
     * 
     * @return the formatted status line
     * 
     * @throws ParseException
     *             in case of a parse error
     */
    CharArrayBuffer formatStatusLine(CharArrayBuffer buffer, StatusLine statline);

    /**
     * Formats a header. Due to header continuation, the result may be multiple
     * lines. In order to generate well-formed HTTP, the lines in the result
     * must be separated by the HTTP line break sequence CR-LF. There is
     * <i>no</i> trailing CR-LF in the result. <br/>
     * See the class comment for details about the buffer argument.
     * 
     * @param buffer
     *            a buffer available for formatting, or <code>null</code>. The
     *            buffer will be cleared before use.
     * @param header
     *            the header to format
     * 
     * @return a buffer holding the formatted header, never <code>null</code>.
     *         The returned buffer may be different from the argument buffer.
     * 
     * @throws ParseException
     *             in case of a parse error
     */
    CharArrayBuffer formatHeader(CharArrayBuffer buffer, Header header);

}
